苏鲁超高压变质带中海阳所地区变基性岩的地球化学性质及变质演化特征  

Geochemical characteristics and metamorphic evolution of metamafic rocks from Haiyangsuo area,Sulu ultrahigh-pressure metamorphic belt

作　　者：刘利双 刘福来[1] 刘平华[1] 蔡佳[1] 施建荣[1,2] 刘超辉[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2015年第10期2863-2888,共26页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目(41430210);国家自然科学基金面上项目(41372069);中国地质调查局地质大调查项目(12120114061901;12120114021401)联合资助

摘　　要：苏鲁超高压变质带的海阳所地区广泛分布各类变基性岩,它们主要由＂红眼圈＂结构的变辉长岩、（石榴）斜长角闪岩组成,且以透镜状或似层状赋存于片麻岩中。根据主量元素和微量元素特征,可将海阳所地区变基性岩划分为两种类型：第一类（A组）样品轻稀土相对富集,其稀土元素配分曲线具有右倾型的特征,微量元素具有Nb、Ta、Zr、Hf、Ti的明显负异常,其蛛网图配分曲线微弱右倾,类似于岛弧玄武岩IAB的特征;第二类（B组）样品稀土元素配分曲线和微量元素蛛网图配分曲线均相对平坦,Nb、Ta、Zr、Hf、Ti略微亏损,与洋中脊玄武岩E-MORB具有一定的相似性。所有变基性岩样品均属于拉斑玄武岩系列,成因类型部分与岛弧环境相关,另一部分则可能与洋中脊环境关系密切。根据岩相学、矿物相转变、变质反应以及温压条件估算的综合研究结果,识别出海阳所变基性岩可能经历了两期变质作用,其中第一期中-高压麻粒岩相变质作用（M1）的标志性矿物组合以基质中保存的粗粒石榴石（Grt1）＋粗粒单斜辉石（Cpx1）＋粗粒斜长石（Pl1）±石英（Qtz）组合为特征,形成的温压条件为T=725～845℃、P=9.5～12.4kbar;第二期峰期高压麻粒岩相变质阶段（M12）以发育＂红眼圈＂结构为特征,典型的矿物组合为新生的细粒石榴石（Grt12）＋单斜辉石（Cpx12）＋斜长石（Pl12）±石英（Qtz）,形成的温压条件为T=765～845℃、P=14.8～17.5kbar,而峰后角闪岩相退变质阶段（M12）以形成低温退变质矿物组合绿色角闪石（Amp22）＋斜长石（Pl22）±石英（Qtz）±石榴石（Grt22）为特征,形成的温压条件为T=575～680℃、P=6.0～8.0kbar。第二期变质演化P-T轨迹具有近等温降压至减压冷却的顺时针型式。海阳所变基性岩记录的多期变质演化的信息及其P-T条件与苏鲁-大别超高压变质带存在明显差异。结�Abundant meta-mafic rocks are distributed in the Haiyangsuo town of the Sulu ultrahigh-pressure metamorphic belt as irregular lenses or layers within the gneisses. These meta-mafic rocks are mainly composed of ＂red-eye cycle＂ meta-gabbros and （garnet） amphibolites. Based on the characteristics of major and trace elements, the meta-mafic rocks in the studied area can be divided into two types. Group A is characterized by enrichments of LREE in the chondrite-normalized REE patterns and negative anomalies of Nb, Ta, Zr, Hf and Ti in the primitive mantle-normalized trace element diagrams, which are similar to the features of IAB. Whereas group B is characterized by relatively fiat patterns in the chondrite-normalized REE diagrams and primitive mantle- normalized trace element diagrams and weakly negative anomalies of Nb, Ta, Zr, Hf and Ti, which are almost consistent with those of E-MORB. All the meta-mafic rocks are tholeiites series and some of them may be related to island arc setting, whereas others are associated with mid-ocean ridge setting. According to petrography, mineral phase transformation, metamorphic reactions and pressure- temperature estimation, two periods of metamorphism have been recognized in the meta-mafic rocks. The first period of metamorphism （M22） shows middle to high-pressure granulite-facies metamorphic event, and the second period of metamorphism include a peak metamorphic stage （ M22 ） and a late amphibolite-facies retrograde stage （ M22 ）. P-T conditions for each stage were estimated using thermo-dynamical and experimental geothemometers and geobarometers. Corase-grained mineral assemblage of garnet （Grh ） ＋ clinopyroxene （ CpxI ） ＋ plagioclase （ P11 ） ＋ quartz is regarded as the typical mineral assemblage of peak metamorphic stage of M1 and yielded P-T conditions of 725 - 845℃and 9. 5 -12.4kbar. The peak metamorphic stage of the second period of metamorphism （ M22 ） is characterized by ＂red-eye cycle＂ texture and typical fine-grained miner

关 键 词：变基性岩 地球化学 多期变质事件 华北克拉通变质基底 苏鲁超高压变质带 海阳所 

分 类 号：P588.34[天文地球—岩石学]